错误代码：1054。“ on子句”中的未知列

Question

The query is meant to return the percentage based on value from one table being divided by the value of another table. However, there is something wrong and I am missing it.

similar problems noted on the board looked related to JOIN, but did not seem to be the problem, when I tried and explicit join -- basically mysql was like -- now you are an idiot-- I must have did that wrong or that is not the problem.

    SELECT (pathogenPop / locationpop) as PercentInfected
       FROM ( 
       (SELECT apinfectcount.APInfectCountInfected 
       as pathogenPop, apinfectcount.APInfectCountLocation
       FROM apstart.apinfectcount 
       GROUP BY apinfectcount.APInfectCountLocation) as pathogenPop

           Inner JOIN 

       (SELECT apcountrypop.apcountrypopPopulation 
       as locationpop, apcountrypop.apcountrypopCountry
       FROM apstart.apcountrypop 
       GROUP BY apcountrypop.apcountrypopCountry) 
       as locationpop
       on apinfectcount.APInfectCountLocation = apcountrypop.apcountrypopCountry 
       and apinfectcount.APInfectCountWeek = 23);

Table Schema: apcountrypop

    idapcountrypop          INT(11)
    apcountrypopCountry     VarChar(45)
    apcountrypopPopulation  FLOAT

Table Schema: apinfectcount

    idAPInfectCount         INT(11)
    APInfectCountLocation   VarChar(45)
    APInfectCountOutBreak   VarChar(45)
    APInfectCountPathogen   VarChar(45)
    APInfectCountInfected   FLOAT
    APInfectCountDead       FLOAT
    APInfectCountWeek       VarChar(45)

If it worked -- it would assign apinfectcount.APInfectCountInfected to pathogenPop and apcountrypop.apcountrypopPopulation to locationpop

for the values where the locations are the same(apinfectcount.APInfectCountLocation = apcountrypop.apcountrypopCountry)

then it would return the value of the apinfectcount table value is divided by the apcountrypop table to give the percentage.

so in this specific example I only have sample data so I am just wanted to return one value so I added the where clause to just test the logic and syntax.

I appreciate the help.

Answer 1

You have assugned the tables alias pathogenPop and locationpop so you need pathogenPop.APInfectCountLocation = locationpop.apcountrypopCountry and pathogenPop.APInfectCountWeek = 23 in ON clause

SELECT (pathogenPop / locationpop) as PercentInfected
     FROM ( 
     (SELECT apinfectcount.APInfectCountInfected 
     as pathogenPop, apinfectcount.APInfectCountLocation
     FROM apstart.apinfectcount 
     GROUP BY apinfectcount.APInfectCountLocation) as pathogenPop

         Inner JOIN 

     (SELECT apcountrypop.apcountrypopPopulation 
     as locationpop, apcountrypop.apcountrypopCountry
     FROM apstart.apcountrypop 
     GROUP BY apcountrypop.apcountrypopCountry) 
     as locationpop
     on pathogenPop.APInfectCountLocation = locationpop.apcountrypopCountry 
     and pathogenPop.APInfectCountWeek = 23) T;

and also a table alias for the outer FROM(..) T

Answer 2

I don't have the database to test against so I'm not 100% certain this will run, but would the following query not be a bit simpler?

SELECT (apinfectcount.APInfectCountInfected / apcountrypop.apcountrypopPopulation) as PercentInfected, apinfectcount.APInfectCountLocation
FROM apinfectcount
INNER JOIN apcountrypop  ON apcountrypop.apcountrypopCountry = apinfectcount.APInfectCountLocation
WHERE  apinfectcount.APInfectCountWeek = 23
GROUP BY apinfectcount.APInfectCountLocation

And I assume there is only one location record per location in each table?

Answer 3

There is an issue within a query. As scope of apinfectcount.APInfectCountLocation column and apcountrypop.apcountrypopCountry column is limited to subquery only you cannot use it outside the subquery (within where clause). You can check out these docs on subquery https://docs.microsoft.com/en-us/sql/relational-databases/performance/subqueries?view=sql-server-2017

Refer code below.

SELECT (countInfected / countrypopulation) as PercentInfected
   FROM ( 
   (SELECT apinfectcount.APInfectCountInfected 
   as countinfected, apinfectcount.APInfectCountLocation, APInfectCountWeek as 
   countweek
   FROM apstart.apinfectcount 
   GROUP BY apinfectcount.APInfectCountLocation) as pathogenPop

       Inner JOIN 

   (SELECT apcountrypop.apcountrypopPopulation 
   as countrypopulation, apcountrypop.apcountrypopCountry
   FROM apstart.apcountrypop 
   GROUP BY apcountrypop.apcountrypopCountry) 
   as locationpop
   on pathogenPop.countinfected = locationpop.countrypopulation
   and pathogenPop.countweek= 23);